Redirect a 404 to another page and capturing the page with .htaccess

Alright, what I'm wanting to do is create a .htaccess that will redirect any 404 error to another page while capturing the path/file attempted to be accessed.

So, if they are trying to access

www.mydomain.com/xxx 

I want it to be redirected to

www.mydomain.com/error.php?e=xxx.  

I've never been overly good at writing .htaccess files so any help someone could provide would be WONDERFUL.

I would need this to work sitewide. Thank you in advance!